The answers given above are correct, but in your snippet,
digitalWrite (LED, HIGH);
delay(1000);
digitalWrite (LED, LOW);
delay(1000);
digitalWrite (LED2, HIGH);
delay(50);
digitalWrite (LED2, LOW);
delay(50);
you aren't driving two leds at the same time. You are switching one on for one second, then switching it off. Then, one second later, you switch the second led on for 50 milliseconds, then switch that one off. That seems to me to agree with your observed results.